Fringed thermal protection device and method of manufacturing it

ABSTRACT

A thermal protection device for protecting walls of structures exposed to ablative flow at high temperatures in the presence of vibrations comprises, embedded in a thermally insulative matrix, a refractory armature formed by a fringed mat comprising a meshed part exposed to the ablative flow and fringes intended to be directed towards the wall of the structure to be protected. The device further comprises an open-weave refractory woven material parallel to the meshed part of the armature and through which the fringes pass.

This is a division, of copending patent application Ser. No. 07/523,674, filed May 15, 1990, now U.S. Pat. No. 5,178,922.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a thermal protection device designed to protect the cylindrical casing of a ramjet engine combustion chamber.

The invention is more particularly concerned with an internal thermal protection device for hollow structures subjected to the ablative flow of corrosive gases at high speeds and high temperatures and to high-level vibrations, in particular where such phenomena are inherent to their operation, and with a method of manufacturing this device.

2. Description of the Prior Art

In the current state of the art the thermal protection layers of such structures are made from composite materials using organic, organo-metallic or mineral binders possibly including powder, fiber, mineral or organic woven reinforcement. When exposed to hot gases the ablatable material is pyrolyzed. This pyrolysis is accompanied by deterioration of the carbon-based or organo-silicic chain of the binder which renders the scoria fragile and breakable within the mass of material. To alleviate this the thermal protection layer is usually reinforced, by various techniques.

It is known that the ablation of a material of this kind subjected to erosion by hot gases and to vibration is reduced when the material is reinforced. The reinforcing armature embedded in the insulating material may be metallic or non-metallic, woven or fibrous.

The patent U.S. Pat. No. 4,655,866 describes a reinforced thermal protection device of this kind and the method of manufacturing it. The device is for thermally protecting walls along which gas flows, such as ramjet engine combustion chambers.

This prior art patent is of interest because it enabled the development of a flexible, for example silicone protection, reinforced in particular by an armature oriented relative to the gas flow, which confers good resistance to ablation and to loss of material due to vibration inherent to operation of the engine.

An object of the invention is to improve the performance of a device as disclosed in the aforementioned patent, in particular with regard to its mechanical strength following pyrolysis of the binder.

SUMMARY OF THE INVENTION

In one aspect, the invention consists of a thermal protection device for protecting walls of structures exposed to ablative flow at high temperatures in the presence of vibrations, the device comprising, embedded in a thermally insulative matrix, (1) a refractory armature formed by a fringed mat comprising (i) a meshed part exposed to the ablative flow and (ii) fringes intended to be directed towards the wall of the structure to be protected, the device further comprising (2) an open-weave refractory woven material parallel to the meshed part of the armature and through which said fringes pass.

The effect of implanting in a fringed mat a woven material in which the threads are advantageously twisted or spiralform (in the form of helical coils) is to maintain the integrity of the scoria after deep pyrolysis of the thermal protection and even after deterioration of its adhesive bonding to the wall to be protected. The effect of the spiralform woven material is to bind the layers of fringes together and to solidify the structure.

Advantageously, the refractory woven material is in the form of interpenetrating parallel spiralform filaments, which makes the woven material very flexible in a direction parallel to the filaments.

The refractory woven material may be chosen from the following materials: steel, carbon impregnated with a resin which stiffens or rigidifies the woven material, hereinafter termed a stiffener resin, silica impregnated with a stiffener resin or some other organic or non-organic resin.

In accordance with non-limiting preferred features of the invention:

the thermally insulative matrix in which the refractory armature is embedded is silicone-based, i.e. a silicone resin forms a substantial part of the matrix,

the matrix is charged with silicon carbide fibers and powder or any other refractory (powder) material,

the fringed mat is made from silicon carbide or any other refractory (fiber) material,

the device is cylindrical and the armature is formed by a fringed tape wound on in a spiral.

In another aspect the invention consists of a method of manufacturing a thermal protection device to protect the inside of a cylindrical wall exposed to ablative flow at high temperatures and in the presence of vibration, in which method:

a fringed refractory tape is wound onto a mandrel so that the fringes are oriented so as to radially project outwardly relative to the mandrel so as to form a fringed mat,

the fringed mat is impregnated with a thermally insulative substance that can be polymerized,

an open-weave refractory woven material is disposed around the impregnated fringed mat,

the filaments of the woven material are caused to penetrate between the fringes of the fringed mat, and

According to non-limiting preferred features of the invention:

the filaments of the woven material are caused to penetrate between the fringes of the fringed mat by winding a filament or tape around the woven material,

the filament or tape is made from a refractory material,

the filament or tape is made from steel,

the filament or tape is made from silicon carbide,

the filament or tape is made from carbon fibers,

the filament or tape is made from silica fibers,

the cured assembly is machined to match the inside diameter of the cylindrical wall to be protected,

it is principally the base of the fringes that are impregnated in order to facilitate penetration of the free ends of the fringes into the woven material,

the curing is carried out under pressure,

the thermally insulative matrix is silicone-based and the curing is carried out at 100° C. at a pressure of 10 bars for one hour 30 minutes,

the fringed tape is silicon carbide based,

the woven material is in the form of interpenetrating parallel spiralform filaments,

the woven material is made from steel.

The performance of a protective material in accordance with the invention depends on the following parameters:

the nature of the fringes (nature and size of the fibers): this is chosen according to the required thickness of the thermal protection, the previously chosen type of structure (woven material) and the depth to which it is applied; the fringes, once wound, must be in a plane as close as possible to the radial plane and the ends of the fringes must not be impregnated (or must be impregnated to only a limited degree) so that said fringes can easily be inserted into the spiralform woven material;

the tension with which the fiber or tape is bound: this tension directly influences the inclination of the fringes and their ability to remain in a radial plane of the mandrel;

the nature and therefore the viscosity of the impregnating substance: a substance with too low a viscosity is not suitable as it may run; the substance must have a consistency such that it wets the fringes perfectly while itself remaining sufficiently thixotropic for the tape to retain its original shape and not to run;

the machine parameters (feed pressure, size and position of the fringes): these are all factors conditioning the obtaining of a correct base for the implantation of the mesh.

Objects, characteristics and advantages of the invention will emerge from the following description given by way of non-limiting example with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a thermal protection device in accordance with the invention.

FIG. 2 is a partially cut away enlarged view of the detail I from FIG. 1.

FIG. 3 is a side view of the device from FIG. 2, as seen in the direction of the arrow III in FIG. 2, in an exploded form showing the main stages in the manufacture of the device.

FIG. 4 is a perspective view of a mandrel around which a fringed tape is wound in a first stage of the method of manufacturing the device from FIGS. 1 through 3.

FIG. 5 is a perspective view showing the tape wound in a previous stage and a piece of woven material on the point of being wound around the mandrel.

FIG. 6 is a perspective view of a refractory tape being wound around the mandrel, the fringed tape and the woven material during another stage in the manufacturing process, in which the fringes on the tape are caused to interpenetrate with the woven material.

DETAILED DESCRIPTION OF THE INVENTION

As is seen from FIGS. 1 through 3 a thermal protection device 1 in accordance with the invention comprises, embedded in a thermally insulative matrix which impregnates it, a refractory armature 2 and an open-weave material 3.

The refractory armature 2 is formed by a fringed mat including a meshed part 4 designed to be exposed to the ablative flow and fringes 5 designed to face towards the wall of the structure to be protected.

The open-weave material 3 comprises interpenetrating parallel spiral filaments 3A.

The spiral filaments 3A are entirely enclosed between the fringes 5 of the armature 2, which therefore pass completely through the open weave of the woven material 3.

The meshed part is advantageously meshed also in the direction of its thickness.

A protection layer 6, advantageously of a refractory nature, is disposed at the ends of the fringes and fixed to them, for example by way of the adhesive natrue of insulative matrix.

This insulative matrix material is advantageously polymerizable.

When, as in the case in FIGS. 1 through 3, the device 1 is part-cylindrical, the spiralform filaments 3A are oriented parallel to the generatrices of the cylinder so that the curvature of the device does not lead to any significant deformation of the spiralform filaments themselves.

FIGS. 4 through 6 show the principal stages in manufacturing this device:

in FIG. 4 a non-impregnated fringed tape 7 is being wound onto a mandrel 8 with a diameter at least equal to the usable inside diameter of the combustion chamber, the mandrel 8 being mounted on a machine 9,

the resulting fringed mat 2 is impregnated by means of a transfer device that is not shown (transfer press and pot or transfer gun, for example applies between rows of fringes a filled silicone resin substance which impregnates the refractory matrix of the protection device (which constitutes the aforementioned insulative matrix),

in FIG. 5 the metal spiralform woven material 3 is being readied for placement over and implantation into the wound and impregnated mat 2;

in FIG. 6 the resulting structure is being bound by winding on a refractory filament or tape 10 constituting the aforementioned layer 6,

the mandrel and the structure wound onto it are put into an autoclave (not shown) and cured at a temperature of 100° C. and a pressure of 10 bars for one hour 30 minutes,

the thermal protection the resultant thermal protection body 1 is machined to thickness, preferably by machining it down to the level of the metal woven material.

The spiralform filaments of the woven material 3 are parallel to the axis of the mandrel.

For this operation to be carried out under optimum conditions:

the ends of the fringes must not be impregnated, or must be impregnated to only a limited degree, so that the fringes can readily penetrate the woven material,

the fringes must be in a plane as close as possible to the radial direction of the mandrel,

the silicone matrix must have a consistency such that the fringes are totally wetted, but it must also be sufficiently thixotropic for the tape to retain its original form and not run.

In one specific embodiment of this thermal protection the materials used are as follows:

    ______________________________________                                         silicon carbide fringes                                                        thread count           1,000 threads/tuft                                      length                 12 mm                                                   base height            3.5 mm                                                  beat-up                3/cm                                                    weight/m               3.8 g                                                   mixture composition (prepared                                                  by any suitable known method):                                                 RTV 630 A              (100 parts)                                             RTV 630 B              (10 parts)                                              Supplier               G.E.                                                    SiC powder             (25 parts)                                              SiC fibers             (6 parts)                                               PR 67 retardant        (2 parts)                                               staniless steel spiralform woven material:                                     void (separation of filaments)                                                                        3 mm                                                    filament diameter      0.6 mm                                                  pitch of spirals       5 mm                                                    ______________________________________                                    

These materials yield a product with the following mean characteristics:

    e.sub.m ≠8.5-9 mm

    d.sub.m ≠1.8 g/cm.sup.3

    λ.sub.m ≠0.53 W/m/°C.

    C.sub.m ≠1.15/g/°C.

where:

e_(m) =mean thickness

d_(m) =mean density

λ_(m) =mean thermal conductivity

C_(m) =mean specific heat

It goes without saying that the foregoing description has been given by way of non-limiting example only and that numerous variant embodiments may be proposed by those skilled in the art without departing from the scope of the invention. 

There is claimed:
 1. A method of manufacturing a thermal protection device to protect the inside of a cylindrical wall exposed to ablative flow at high temperatures and in the presence of vibration, which method comprises:winding a fringed refractory tape onto a mandrel so that the fringes are oriented radially relative to said mandrel so as to form a fringed mat, impregnating said fringed mat with a thermally insulative substance, disposing an open-weave refractory woven material around the impregnated fringed mat, causing the filaments of the woven material to penetrate between the fringes of the fringed mat, and curing the resulting assembly.
 2. A method according to claim 1, wherein said causing step comprises winding a filament or tape around said woven material.
 3. A method according to claim 2, wherein said filament or tape is made from steel.
 4. A method according to claim 3, wherein said filament or tape is made from steel.
 5. A method according to claim 3, wherein said filament or tape is made from silicon carbide.
 6. A method according to claim 3, wherein said filament or tape is made from carbon.
 7. A method according to claim 3, wherein said filament or tape is made from silica.
 8. A method according to claim 1, further comprising machining the cured assembly to match the inside diameter of the cylindrical wall to be protected.
 9. A method according to claim 1, wherein said impregnating step comprises principally impregnating the base of said fringes in order to facilitate penetration of the free ends of said fringes into said woven material.
 10. A method according to claim 1, wherein said curing step is carried out under pressure.
 11. A method according to claim 10, wherein said thermal protection device is silicone-based and said curing step is carried out at 100° C. and at a pressure of 10 bars for one hour 30 minutes.
 12. A method according to claim 1, wherein said fringed tape is silicon carbide based.
 13. A method according to claim 1, wherein said woven material is in the form of interpenetrating parallel spiralform filaments.
 14. A method according to claim 13 wherein said woven material is made from steel. 